Collaborative Research: Levantine geomagnetic field spike: How high, how fast, how far?

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Mining activity has left enormous piles of material in numerous places around Europe and Asia spanning the last seven millennia. Because copper smelting requires melting of ore at high temperatures in furnaces, there is abundant charcoal intimately associated with the copper slag, enabling the direct dating of the archaeological debris. It turns out that metallurgical debris can retain an excellent record of the ancient geomagnetic field strength. This, combined with unprecedented ability to date the material, means that high resolution records of changes in field strength are now available to us. We have already documented a period of time in Jordan (10th century BCE) of extraordinarily high magnetic field strengths, nearly three times the present field. This geomagnetic field "spike" must have happened very quickly. Comparison of these data with those from nearby studies in Greece suggest that there is a significant discrepancy between the Grecian master curve and the data from Jordan. To assess the various possible causes for this discrepancy (e.g., extremely short wavelength features in the geomagnetic field, extremely high frequency temporal changes in the geomagnetic field missed, etc.), we are excavating a second site near to and co-eval with the site containing the "spike" and a co-eval site in Cyprus that has comparable material. The combination of archaeology and the study of the ancient geomagnetic field (paleomagnetism) is inherently interdisciplinary, with broad impacts in both disciplines. Interdisciplinary research is difficult in practice because graduate students need to become expert in their own fields and run the risk of becoming too broad at the expense of depth. We are handling this problem in our research by having two graduate students work closely together, each firmly rooted in one discipline but learning a great deal about the other discipline from the other student. The benefits of such interdisciplinary efforts are wide ranging. From the point of view of studying the geomagnetic field, an accurate picture of intensity changes on a global scale (a goal to which this project contributes but does not solve by itself) is essential for such different endeavors as "ground truthing" numerical models and understanding variations in the production of radiocarbon and the calibration of the radiocarbon time scale. From the archaeological perspective, placing archaeological materials in a tight temporal framework is always a challenge and our work is already being put to use to solve dating puzzles in archaeometallurgy.